Vaccination is the single most important measure for preventing yellow fever. Yellow fever vaccine is safe and effective and provides immunity within one week in 95% of those vaccinated. Yellow fever control is based on the prevention of outbreaks, and this can only be achieved if the majority of the population is immunized. A two-pronged strategy is used to achieve this goal.

The first strategy is the inclusion of the yellow fever vaccine in national childhood routine immunization programmes, to be administered at 9 months of age, simultaneously with the measles first dose. However, reaching the desired level of population immunity takes more than 30 years with infant routine immunization only, even with a high coverage. Therefore this strategy needs to be combined with the implementation of mass preventive vaccination campaigns to rapidly increase the population's immunity and to protect susceptible older age groups in selected high risk areas.

During yellow fever epidemics, outbreak response vaccination campaigns are carried out with minimum delay in order to limit the spread of the disease.

In 2000, a global shortage of yellow fever vaccines for outbreak response arose from the long lead-time needed to produce the vaccine and poor surveillance and reporting which mask trends and make the forecasting of vaccine needs especially difficult.

With vaccine manufacturers as partners in the ICG, a stockpile of 2 million doses reserved for outbreak response was established. The yellow fever ICG sub-group evaluates requests for yellow fever vaccine based on agreed criteria for vaccine provision. If the criteria are fulfilled, doses are released from the stockpile for emergency control of the outbreak.

The Global Alliance for Vaccine and Immunization (GAVI) support

As demands for the use of the stockpile increased, a joint WHO-UNICEF proposal was successfully presented to the Global Alliance for Vaccine and Immunization (GAVI) Board in 2003 for financing an increased global stockpile of 6 million doses per year for a period of 3 years. In July 2005, GAVI support has been extended for an additional year until 2006.

Use of the vaccine stockpile

This mechanism will ensure that all available vaccine stocks are directed to the areas of most urgent need and that adequate supplies are manufactured and stockpiled against future outbreaks.

Since the accumulation of the first stockpile in August 2003, the GAVI global vaccine stockpile has been successfully used in the outbreaks of urban yellow fever in Cote d’Ivoire, Colombia, Liberia, Senegal and Sierra Leone.

In September 2001, yellow fever cases were confirmed in five of the ten communes in Abidjan; suspected cases were also reported elsewhere. Urban yellow fever, although very rare, can spread extremely rapidly among a dense urban population, causing many thousands of deaths and very serious humanitarian consequences. Over 3.5 million people live in Abidjan – the commercial capital of Cote d’Ivoire.

WHO, working closely with UNICEF, coordinated the international response team with partners in the Global Outbreak Alert and Response Network (GOARN). An Operations Centre was established at the WHO office in Abidjan to coordinate activities in epidemiology, the immunization campaign, and vector control. Global reserve stock and delivery of vaccines and supplies were through the yellow fever sub-group of the International Coordinating Group for Emergency Vaccine Provision.

An outbreak of yellow fever occurred between December 2003 and January 2004 in the States of Cesar, Magdalena and La Guajira (28 cases, including 11 deaths, 39% case-fatality rate).

These cases took place in the very popular tourist region of Sierra Nevada de Santa Marta, with a major impact on tourism as 5 national parks were closed to visitors. This outbreak followed an outbreak of epizootic disease among monkeys in the Los Besotes natural park in Cesar State.

Three million doses of yellow fever vaccine were used in the epidemic response, with the objective of providing immunization coverage for 100% of subjects aged over 1 year in urban and rural areas: 500 000 doses were donated by Venezuela, 1.5 million came from Brazil and 1 million from the GAVI global stockpile.